That's the insignia of 303. Squadron, which fought in the battle of Britain.

This logo first appeared during Polish-bolshevik war and was used by 7th Fighter Escadrille, in which American volunteers served (including Merian C. Cooper, the director of King Kong). It presents American stripes (which happen to correspond with Polish flag's colors) and stars, and crossed scythes (popular peasant weapon during Kosciuszko uprising) under a hat worn by T. Kosciuszko during said insurgency. After the 1920, it was adapted by 111th Fighter Escadrille, from which many pilots of 303. Squadron originated, and was then chosen as the Squadron's official emblem.

Currently the traditions of 303. Squadron are continued by 1st Tactical Squadron, which operates MiG-29s, including this one. It's tail fin also has a portrait of Miroslaw Ferić, one of 303. Squadron pilots.

Sorry to disappoint you, but the Poles in Britain never had a 254th Squadron. Polish RAF squadron (including all types - bomber, fighter and liaison) recieved numbers: from 300 to 309, from 315 to 318, and the only exception were 663. Air Observation Post Squadron, as well as 138. and 1586. (Special Duties) Squadrons. The 302. and 303. Squadrons were the ones to participate the most in battle of Britain.

If you really have something about Poles flying in 254. Squadron, feel free to share, because that'd be a new piece of information for me. From what I see, 254. Squadron was not a fighter, but an anti-submarine unit. Of course it could be that some Poles could join other, non-Polish squadrons, but the ones I mentioned were completely Polish.Plus here in Poland, we're taught about 303. Squadron and other Polish units since primary schools. If you haven't read it already, I really recommend Arkady Fiedler's "303. Squadron", it's an epic book about the exploits of that formation, I think it was translated to English several times.